Field of the Invention
The invention relates to a grease filter made from metal, in particular, for use in commercial kitchens and in household vapor extractor hoods.
Grease filters of this type are known. They have a first row of profiles disposed at distances from one another and open in the direction of the gas flow and also a second row of profiles disposed at distances from one another and open opposite to the direction of the gas flow, the mutually adjacent longitudinal edges of two juxtaposed profiles of one row projecting in each case into the inner space of an opposite profile of the other row.
Filters of this type are described in German Patent DE 27 20 201 C2 and U.S. Pat. No. 3,910,782 to Struble et al. (hereinafter “Struble”). In the Struble separation grids, the distance between the two profile rows is dimensioned such that the air flowing through experiences a multiple reversal of direction. The free passage cross-section is 10-30% of the entire grid area, depending on the type of separation grid. As a result of this reduction in cross-section within the separation grid, an increase in the air velocity of 3-10 times occurs. The separating action of the grid is based on this velocity increase. As a result, the liquid droplets and solid particles contained in the air are, of course, also accelerated, and on the multiple reversal in direction of the air flowing through. The accelerated liquid droplets and solid particles cannot follow the change in direction and impinge onto the inner surface of the profiles of the second row. The liquid droplets form on its surface a liquid film that is intended gradually to run off downward and pass through special orifices in the frame of the separation grid into a collecting rail disposed below the separation grid.
Due to the oblique position of the separation grids in the extractor hoods, the liquid film does not, for the large part, run downward in the profile direction, as desired, but, instead, even after a short travel, arrives at the two edges of the profiles. There, the liquid film is intercepted by the air flowing through between the profiles at a high velocity. Depending on the kinematic viscosity of the liquid film, particles of greater or lesser size are torn out of the liquid film and, thus, enter the spent-air stream. The desired separating action is absent or is greatly impaired.
It is proposed, in German Published, Non-Prosecuted Patent Application DE 44 27 074 A1, that the longitudinal edges of the profiles of the second row be bent inward to form gutters such that, when the separation grid is in operation, these gutters form dead-flow spaces in which a drainage of the separated particles takes place.
It, then, became known from German Utility Model DE 299 06 295 U1 to configure an additional filter as a unit mechanically releasable from the air vortex filter. The additional filter is of a knitted fabric filter and is disposed behind the tray-shaped elongate guide plates. Due to the releasable connection to the air vortex filter, the additional filter is removable and can be cleaned or exchanged.
Contrary to this direction of development, German Utility Model DE 298 11 000 U1 proposes a grease trap filter using two or more layers of a grid that has slot bridges produced on both sides of a plate by a punching operation, the grids being disposed within the filter such that the slot bridges run vertically or obliquely downward, and the grids being held together by a common frame. A further grid, the slot bridges of which are disposed horizontally, may be located in each case between two grids having slot bridges running vertically or obliquely downward.
The disadvantage of these filter configurations is that the impact filters have only insufficient grease efficiency, and the following releasable knitted fabric filter insert according to German Utility Model DE 299 06 295 U1, in turn, provides only insufficient protection against flame puncture. Furthermore, here, a measurement transducer is disposed, which is intended to cause signal emission dependent on differential pressure. This signifies additional outlay in measurement terms, and the safety actually capable of being achieved is dubious.
In addition, these filter configuration do not leave any latitude for secondary noise protection measures.